Method of increasing infrared sensitivity



J A. P. H. TRIVELLII ETAL 2,

METHOD OI INCREASINGINFRARED SENSITIVITY Filed April 28, 1939 RED AND .INFRA-RED smsmvc EMULSION CONTAINING -A HYDRAZINE, SEMICARBAZIDE, OR SEMICARBAZONE SUPPORT nlwexrviomd Adrian PH.Trivelli Burt H. Carroll Patented June 10, 1941 PATENT OFFICE METHOD OF INCREASING INFEARED SENSITIVITY Adrian P. H. 'lrivelli and Burt H. Carroll, Rochester, N. Y., assignors to Eastman Kodak Company, Rochester. N. Y., a corporation of New Jersey Application April 28, 1939, Serial No. 270,588

6 Claims.

This invention relates to photographic emulsions and more particularly to a method for increasing the red and infra-red sensitivity and the stability of emulsions.

It is known that reducing agents or halogen absorbers may be added to photographic printout emulsions for the purpose of increasing the printing-outspeed. Use of semi-carbazide salts for this purpose is described in Falleson and Stand U. S. Patent No. 2,126,316, August 9, 1933. Reducing agents of this type are of little value, however, in increasing the sensitivity of emulsions used for making developed images. For exposure within the ordinary range, that is, short of solarization, and for emulsion; of sensitivity suitable for negatives, no improvement can be eilfected in this way if the emulsion has not been sensitized by sensitizing dyes and little or no im provement ordinarily can be brought about if the emulsion has been sensitized to the visible region of the spectrum.

We have found that sensitization to the red, deep red and infra-red regions of the spectrum can be improved by the addition of certain reducing agents to the emulsion prior to coating. A further improvement brought about in this way is an increase in the stability of the sensitizing. Emulsions sensitized to the infra-red commonly tend to lose a' large proportion of this sensitivity within a few months after coating and we have found that this loss can be greatly diminished by adding certain reducing agents to the emulsion.

In the accompanying drawing, the single figure is asectional view of a photographic element having a red and infra-red sensitive emulsion stabilized according to our invention.

It is an object o! the present invention to provide a photographic emulsion having increased sensitivity to the red and infra-red region the spectrum. A further object is to provide a red and infra-red sensitive emulsion having improved stability characteristics. A still further object is to provide a novel developing out red sensitive and infra-red sensitive photographic emulsion. Other objects will appear from the following description of our invention.

'Iheseobjectsare accomplishedbyaddinl toa silver halide photographic emulsion sensitized to theredandinira-redregionsofthespectrmn with optical sensitizing dyes, a reducing agent such as hydrazine, seml-carbazide. semi-carbarone or their salts.

Acordlng to our invention, a silver halide emulsion is sensitized with an optical sensitizing dye which extends the sensitivity into the red and 65 20 dicarbocyanines,

10 for use in this way are amino compounds such as hydrazine, semi-carbazide, and their salts such as hydrazine sulfate and semi-carbazide hydrochloride, and the reaction products of semicarbazide with aldehydes or ketones, for example acetone semi-carbazone.

The photographic emulsions used according to our invention may be sensitized with various red and infra-red optical sensitizing dyes such as 4,4-carbocyanines, thiadicarbocyanines, thia-2- dibenzothiadicarbocyanines, thiatricarbocyanines, selenatricarbocyanines, 2,2-dicarbocyanines, unsymmetrical diand tricarbocyanines, merodicarbocyanines, oxatricarbocyanines, and dibenzoxadicarbocyanines.

These sensitizing dyes, as well as others suitable for use according to our invention, extend the sensitivity range of the emulsion so that the maximum sensitivity in the red and infra-red region is for radiation of wave lengths greater than about 700 millimicrons.

The following examples, which are illustrative only, indicate methods of producing stable sensitized emulsions according to our invention.

3 Example 1 fore coating there was added 0.35 gram per liter of semicarbazide hydrochloride. After incubation for seven days at a temperature of 120 F. the control had lost over 50% or its speed and considerable contrast while the emulsion contalnln: the semi-carbazlde hydrochloride had Gained slightly in speed and contrast without any more fog than the control.

Example 2 A gelatino silver halide emulsion was sensitized with an appropriate amount of 1,1p-hydroxy- .2,2'-diethylthiatricarbocyanine. Part of this emulsion was kept as a control and to another part there was added 1.25 grams per liter of acetone semi-carbazone. After incubation oi that of the control without an increase in fog.

Example 3 A gelatino silver halide emulsion was sensitized with 2,2-diethy1thiadicarbocyanine in appropriate concentration. Part of the emulsion was kept as a control and to another part there was added 0.05 gram per liter of hydrazine sulfate. After incubation 'ior seven days at 120 F., the sensitivity of the portion containing the hydrazine sulfate was found ,to be more than double that oil the control, without an increase in fog.

In preparing the emulsions according to our invention, both the optical sensitizing dyes and the reducing agents are added to the emulsion before coating rather than bathing the emulsion after coating. When silver halide emulsions are bathed alter coating, some of the soluble bromides are removed from the emulsion and a change in the silver ion concentration results. There is, however, no change in the silver ion concentration when the sensitized dyes and reducing agents are added to the emulsion before coating.

The single figure of the accompanying drawing illustrates a photographic element made according to our invention. As shown therein, l is a support of glass, cellulosic compound such as cellulose acetate, a synthetic resin, or paper. On the support I there is coated a silver halide emulsion 2 sensitive to the red and infra-red regions oi the spectrum and containing a hydrazine semicarbazide or semi-carbazone. It will be understood that the element may also have other layers such as subbing layers, anti-halation or backing layers, or overcoating layers.

The emulsions used according to our invention will usually be of the gelatino-silver halide type,

although the halide may be dispersed in agentsother than gelatin, such as cellulose mixed esters, synthetic resins, or collodion.

It is to be understood that the examples included in the above specification are illustrative only and that our invention comprises all modifications and equivalents coming within the scope oi the appended claims.

We claim:

1. The method or increasing the sensitivity and stability of a silver halide emulsion sensitized with a polymethine-cyanine dye containing at least seven carbon atoms between two cyanine nitrogen atoms and sensitizing to the red and infra-red regions of the spectrum, which comprises mixing therewith prior to coating an amino compound selected from the group consisting of hydrazines, semicarbazides, and semicarbazones. 2. The method of increasing the sensitivity and stability or a silver halide emulsion sensitized with a polymethine cyanine dye containing at least seven carbon atoms between two cyanine nitrogen atoms and sensitizing to the red and infra-red regions oi? the spectrum which comprises mixing therewith prior to coating a semicarbazide.

3. A method or increasing the sensitivity and stability of a silver halide emulsion sensitized with a 2,2'-dialkylthiadicarbocyanine to the red and infra-red regions of the spectrum, which comprises mixing a hydrazine therewith prior to coating.

4. A 'gelatino-silver halide emulsion sensitized to the-red and infra-red regions of the spectrum with a polymethine cyanine dye containing at least seven carbon atoms between two cyanine nitrogen atoms, containing an amino compound selected from the group consisting oi hydrazines, semicarbazides and semicarbazones.

5. A gelatino-silver halide emulsion sensitized to the red and infra-red regions of the spectrum with a polymethine cyanine dye containing at least seven carbon atoms between two cyanine nitrogen atoms, containing a semicarbazone.

6. A gelatino-silver halide emulsion sensitized with a 2,2'-dial'kylthiadicarbocyanine and containing a hydrazine to increase the stability and the red and infra-red speed.

ADRIAN P. n. 'mrvnim. BURT n. caaaom Cerhfi date of Correction Patent No. 2,245,236. June 10, 1941.

- ADRIAN P. H. TRIVELLI ET AL.-

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 1, second column, line 51, Example 2, for 1,1'fl-hydroxyrear; 3,3'-dim-ethyZ-; and that the said Letters Patent should be read with this correction therein that the same may. conformtothe record of the case inthe Patent Ofiice Signed and sealed this 19th day of August, A. 1941.

HENRY VAL ABSDALE,

Acting C'omam'saioner of Patents. 

